Articles which have organic photochromic material(s) applied to or incorporated therein are characterized in that upon exposure to electromagnetic radiation or to solar light they exhibit a reversible change in color and in light transmission. Once the exposure to the original radiation has been discontinued, the composition returns to its original color, or colorless state. Recently, photochromic plastic materials, most notably, such compositions which may be suitable for the preparation of ophthalmic lenses, films and automotive head lamp lenses have been the focus of attention in the relevant arts. Plastic materials as the medium for the preparation of such lenses allow for the preparation of lighter and thinner lenses than do the traditionally used glass. Also of interest are the applications of photochromic technology to automotive, aircraft transparencies and greenhouse architecture and other glazing applications. It is known that photochromic behavior may be imparted to glass and to certain plastic materials by using inorganic and organic dyes respectively. Photochromic articles prepared from synthetic organic resins such as homopolymers of a poly(allyl carbonate) monomer are known (U.S. Pat. Nos. 4,994,208, 5,246,630, 5,221,721 and 5,200,483).
U.S. Pat. No. 5,244,602 describes a naphthopyran useful for photochromic polymers and also organic hosts such as polyurethanes for such materials. However, a detailed description of the polyurethane is not given.
In McBain, et al. (U.S. Pat. No. 4,994,208), it was demonstrated that photochromic performance of matrices prepared by the free radical polymerization of polyol (allyl carbonates), e.g., diethylene glycol bis(allyl carbonate), could be improved by the incorporation of 10 to 40 weight percent of an aliphatic polyurethane having terminal ethylenic unsaturation. The polyurethanes described in this reference can be represented by the following expression: